The objectives of this project are unchanged from the original proposal and include in the second year: (1)\the production of monoclonal antibodies that inhibit the in vitro cytolytic activity of human cytotoxic T-cell lines; and (2)\characterization of lymphocyte function associated antigens (LFA) in the human cytotoxic T-cell reaction. Mice and rats have been immunized with long-term human cytotoxic cells and antigen preparations derived from these cell lines, and splenocytes from such animals will be fused with X63 myeloma cell line. Primary screening system for identifying monoclonal antibodies will be by inhibition of the 51Cr-release microcytotoxicity assay and will include positive controls for blocking. LFA-1 and T8 surface molecules will be extensively characterized for their function in the cytolytic reaction, using monoclonal antibodies and cloned human CTL lines. Studies directed at further establishing a functional link between LFA-1 and T8 molecules will be undertaken. (CS)